[K0SM0S]

This is precisely what we don't know. If you're talking averages, then sure it takes decades to observe a meaningful change. However climate change of the sort we're anticipating now isn't about averages. It's about peaks, it's about records, and possibly major shifts in equilibrium.

Basically what we witness so far and will keep on seeing are spikes in all directions of the spectrums (e.g. record high temps, but also record lows; rain in the Death Valley and droughts in formerly wet areas). More critically, what little we've been able to gather on how fast climate eras shift from one to the next, it appears that whereas in-cycle change happens rather slowly (change within an era, because averages), climate era shifts could happen very quickly (because chain of events). We're talking going from a warm era to a glacial one within a few years, sometimes months even. A high speculation is that some thongs might upset the Gulfstream and you'd observe climate evolve from year to year.